MAX16922_10 Datasheet, PDF (13/17 Pages) Maxim Integrated Products – 2.2MHz, Dual, Step-Down DC-DC Converters, Dual LDOs, and RESET

2.2MHz, Dual, Step-Down DC-DC
Converters, Dual LDOs, and RESET
Typical Applications Circuit
VBAT
0.1µF
220µF
4.7µF
V_OUT1
PV1
EN
PWM
OUTS2
LX2
PGND2
2.2µH
V_OUT2
10µF
4.7µF
4.7µF
V_OUT2
4.7µF
4.7µF
PV3
PV2
MAX16922 ^BST
OUT3
GND1
GND3
LX1
OUTS1
PV4
OUT4
LSUP
GND
GND2
RESET
EP
4.7µF
0.1µF
4.7µH
V_OUT1
10µF
V_OUT1
1µF
20kΩ
Applications Information
Power-On Sequence
When the EN input is pulled high and PV1 is greater
than 3.7V (typ), the 5V LSUP linear regulator turns on.
Once LSUP exceeds 2.5V, the internal reference and
bias are enabled. When the internal bias has stabilized
OUT1, soft-start is initiated. After completion of soft-start
on OUT1 (2.8ms typ), OUT2 soft-start is initiated. OUT3
soft-start is enabled when PV3 is greater than or equal
to 1.25V (typ), and OUT4 soft-start is enabled when PV4
is greater than or equal to 1.5V (typ).
Care must be taken when driving the EN pin. Digital
input signals deliver a fast edge that is properly detect-
ed by the MAX16922. If driving the EN pin with an ana-
log voltage that has a slew rate of less than 1V/ms or a
voltage-divider from PV1, then the input voltage on PV1
must always be less than 6V when the voltage at EN is
near the turn-off threshold of 1.6V. If this cannot be
guaranteed, then a 1kΩ resistor or 5.6V zener diode
must be placed in parallel with the LSUP output capaci-
tor to prevent possible damage to the device.
Power-Down and Restart Sequence
The MAX16922 can be shut down by thermal shut-
down, enable low (EN), LSUP regulator undervoltage,
or when PV1 falls below 3.0V (typ). When a shutdown
occurs, all outputs discharge through an internal resis-
tor connected between each output and ground. When
enable is high, the die temperature is okay, the LSUP
linear regulator is greater than 2.5V (typ), and OUT1 is
less than 1.25V (typ); a complete soft-start power-on
sequence is reinitiated.
Inductor Selection
The OUT1 step-down converter operates with a 4.7µH
inductor and the OUT2 step-down converter operates
with a 2.2µH inductor. The inductor’s DC current rating
must be high enough to account for peak ripple current
and load transients. The step-down converter’s archi-
tecture has minimal current overshoot during startup
and load transients. In most cases, an inductor capable
of 1.3 times the maximum load current is acceptable.
For optimum performance choose an inductor with DC-
series resistance in the 50mΩ to 150mΩ range. For
higher efficiency at heavy loads (above 400mA) and
minimal load regulation, the inductor resistance should
be kept as small as possible. For light-load applications
(up to 200mA), higher resistance is acceptable with
very little impact on performance.
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